feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/esp-hal/src/config.rs

@@ -0,0 +1,60 @@
+//! # Configuration
+//!
+//! ## Overview
+//! This module contains the initial configuration for the system.
+//!
+//! ## Configuration
+//! In the [`esp_hal::init()`][crate::init] method, we can configure different
+//! parameters for the system:
+//! - CPU clock configuration.
+//! - Watchdog configuration.
+//!
+//! ## Examples
+//!
+//! ### Default initialization
+//!
+//! ```rust, no_run
+#![doc = crate::before_snippet!()]
+//! let peripherals = esp_hal::init(esp_hal::Config::default());
+//! # }
+//! ```
+//! 
+//! ### Custom initialization
+//! ```rust, no_run
+#![doc = crate::before_snippet!()]
+//! let mut config = esp_hal::Config::default();
+//! config.cpu_clock = CpuClock::max();
+//! config.watchdog.rwdt =
+//!     esp_hal::config::WatchdogStatus::Enabled(fugit::MicrosDurationU64::millis(1000 as u64));
+//! let peripherals = esp_hal::init(config);
+//! # }
+//! ```
+
+/// Watchdog status.
+#[derive(Default, PartialEq)]
+pub enum WatchdogStatus {
+    /// Enables a watchdog timer with the specified timeout.
+    Enabled(fugit::MicrosDurationU64),
+    /// Disables the watchdog timer.
+    #[default]
+    Disabled,
+}
+
+/// Watchdog configuration.
+#[non_exhaustive]
+#[derive(Default)]
+pub struct WatchdogConfig {
+    #[cfg(not(any(esp32, esp32s2)))]
+    /// Enable the super watchdog timer, which has a trigger time of slightly
+    /// less than one second.
+    pub swd: bool,
+    /// Configures the reset watchdog timer.
+    pub rwdt: WatchdogStatus,
+    /// Configures the `timg0` watchdog timer.
+    pub timg0: WatchdogStatus,
+    #[cfg(timg1)]
+    /// Configures the `timg1` watchdog timer.
+    ///
+    /// By default, the bootloader does not enable this watchdog timer.
+    pub timg1: WatchdogStatus,
+}